In small internal combustion engines, such as those used to provide the driving force for powered equipment (e.g., lawnmowers, snow blowers), a timing belt is commonly used to connect the crankshaft to the camshaft(s), which in turn controls the opening and closing of the engine's valves. In one particular configuration, a powder metal (PM) timing gear can be pressed onto the crankshaft to drive timing belt to thereby control the overhead cam system. In such a configuration, friction is the only resistance that prevents motion relative to the crankshaft, but where the PM gear is well-made and properly sized, this arrangement can provide good, reliable performance. Ensuring proper sizing can have the tendency to increase manufacturing time on the crankshaft production line, however, and such a configuration can be relatively expensive to produce. In addition, the cost of the PM gear can be relatively high, and manufacturing efficiency is not a good as it could be.
In another common configuration, a timing gear can be slip-fit onto a shaft portion of the crankshaft and held in position by engaging a machined slot formed in the shaft portion. In particular, a protrusion on the timing gear can be engaged with a keyway on the shaft portion of the crankshaft such that the timing gear is mounted at a predetermined angular relationship with respect to the crankshaft. In such a structure, however, a torsional stress due to a driving torque can tend to occur on the keyway of the crankshaft, which can thereby create a tendency of breakdown of the crankshaft along the keyway.
As a result, it would be desirable for an alternative configuration for coupling a timing gear to a crankshaft that is easier to assemble and more cost-effective than a press-fit PM gear but more reliable than simple slot-and-key connections.